Du Yi-Ling, Dalisay Doralyn S, Andersen Raymond J, Ryan Katherine S
Department of Chemistry, University of British Columbia, Vancouver, BC V6T 1Z1, Canada.
Chem Biol. 2013 Aug 22;20(8):1002-11. doi: 10.1016/j.chembiol.2013.06.013. Epub 2013 Aug 1.
Padanamides are linear tetrapeptides notable for the absence of proteinogenic amino acids in their structures. In particular, two unusual heterocycles, (S)-3-amino-2-oxopyrrolidine-1-carboxamide (S-Aopc) and (S)-3-aminopiperidine-2,6-dione (S-Apd), are found at the C-termini of padanamides A and B, respectively. Here we identify the padanamide biosynthetic gene cluster and carry out systematic gene inactivation studies. Our results show that padanamides are synthesized by highly dissociated hybrid nonribosomal peptide synthetase/polyketide synthase machinery. We further demonstrate that carbamoyltransferase gene padQ is critical to the formation of padanamide A but dispensable for biosynthesis of padanamide B. Biochemical investigations show that PadQ carbamoylates the rare biosynthetic precursor l-2,4-diaminobutyrate, generating l-2-amino-4-ureidobutyrate, the presumed precursor to the C-terminal residue of padanamide A. By contrast, the C-terminal residue of padanamide B may derive from glutamine. An unusual thioesterase-catalyzed cyclization is proposed to generate the S-Aopc/S-Apd heterocycles.
帕达酰胺是一类线性四肽，其结构中不含蛋白质原性氨基酸。特别地，在帕达酰胺A和B的C末端分别发现了两个不寻常的杂环，即（S）-3-氨基-2-氧代吡咯烷-1-甲酰胺（S-Aopc）和（S）-3-氨基哌啶-2,6-二酮（S-Apd）。在此，我们鉴定了帕达酰胺生物合成基因簇并进行了系统的基因失活研究。我们的结果表明，帕达酰胺是由高度解离的混合非核糖体肽合成酶/聚酮合酶机制合成的。我们进一步证明，氨甲酰转移酶基因padQ对帕达酰胺A的形成至关重要，但对帕达酰胺B的生物合成是可有可无的。生化研究表明，PadQ将罕见的生物合成前体L-2,4-二氨基丁酸氨甲酰化，生成L-2-氨基-4-脲基丁酸，这是帕达酰胺A C末端残基的推测前体。相比之下，帕达酰胺B的C末端残基可能来源于谷氨酰胺。有人提出一种不寻常的硫酯酶催化环化反应来生成S-Aopc/S-Apd杂环。
